The present invention relates to a technique for suppressing oscillation of an actuator arm to improve a position controlling performance for a magnetic head in a rotating disk storage device such as a magnetic disk drive or a magneto-optical disk drive. More specifically, it relates to a technique for not only suppressing oscillation of an actuator arm but also suppressing flutter of a magnetic head to improve a position controlling performance for the magnetic head.
In a magnetic disk drive as an example of a rotating disk storage device, a head gimbal assembly (hereinafter referred to as “HGA”) is attached to an actuator arm of a carriage, the carriage being driven by a voice coil motor (hereinafter referred to as “VCM”) for pivotal movement. A head/slider composed of a magnetic head and a slider is attached to a front end of the HGA. An air bearing surface (hereinafter referred to as “ABS”) is formed on the head/slider on the side opposed to a recording surface of a magnetic disk. The HGA comprises a spring structure called a flexure to which the head/slider is attached and a load beam which supports the flexure and which applies a pushing load to the head/slider.
When the ABS of the head/slider undergoes a lifting force from an air flow created on the recording surface of the rotating magnetic disk, the head/slider flies at a very slight height over the recording surface of the magnetic disk while being supported by the flexure and performing pivotal movement. Servo data are stored on the recording surface of the magnetic disk. A control unit calculates an error between a central position of a track and the present position thereof from the servo data read by the head and then controls an electric current to be fed to the VCM so that the head may be positioned to the center of the track. Oscillation or shock may be applied to the head, causing an unexpected displacement of the head, while the control unit performs a servo control of follow-up motion for the head. In this case, a longer time than necessary may be consumed until the head is positioned to a predetermined track or the head may perform a follow-up motion while moving with a large amplitude radially relative to the center of the track, thus making read or write difficult.
With the recent improvement in recording density of the magnetic disk drive, the accuracy required for positioning a head to a predetermined track is becoming more and more severe. While a head performs a track follow-up motion for read or write of data, an air flow created on a recording surface of a magnetic disk strikes against an actuator arm and its velocity changes. Upon occurrence of a change in air flow velocity in the vicinity of the actuator arm, oscillation occurs in the actuator arm and is transmitted to the HGA, thus affecting the head position control.
Displacement modes which occur during oscillation of the actuator arm include bending, sway, and torsion. Bending represents a displacement of the actuator arm in a direction perpendicular to the magnetic disk surface, sway represents a displacement in the pivoting direction of the actuator arm, and torsion represents a displacement in the direction of rotation around a center line which is imagined in the longitudinal direction of the actuator arm. Oscillation of the actuator arm caused by an air flow is herein termed flutter. As the rotational speed of the magnetic disk increases, the air flow velocity increases and the flutter in all of bending, sway and torsion modes increases. Furthermore, as the number of stacked magnetic disks is increased, that is, the number of actuator arms is increased, the influence of air flow on the entire carriage becomes more serious and the flutter further increases.
Patent Literature 1 (U.S. Pat. No. 5,854,725) discloses a technique wherein a guide member is attached to a side portion of an actuator arm to diminish the influence of an air flow created from a magnetic disk on the actuator arm. Patent Literature 2 (Published Patent Application US2003/0016473) discloses a technique wherein an actuator arm is tapered on its leeward side to diminish the formation of an eddy and thereby suppress oscillation of the actuator arm.